Floor plan - Conversion into a granny flat experiences?

And make sure whether it is legally possible at all. Do you live in a purely residential area or a mixed area where commercial use is permitted?

Do you live in a purely residential area or a mixed-use area where commercial activities are allowed?

I would also consider a physiotherapy practice possible in a WA, but with a WR you will rightly suspect that it would not be allowed there.

1 WC, 1 room 15sqm, 1 room 8sqm, 1 small storage room 3-5 sqm as well as 1 small reception.

And what is so difficult now to answer the questions from and me? What happens in the rooms? What absolutely must be included and will it be used? 15sqm can be designed as 2.5x7 m or as 3x5 WC ... where should it be accessible from? Is it tied to the position where the bathroom is currently marked? Is the entrance door already there? Could it be placed at the position of the floor-to-ceiling window? Because presumably the 15+ 8 sqm rooms should have windows.

It was unfortunately designed as a granny flat. Everything is drywall, so something also needs to be changed on the floor. The change of use is a formality and has already been applied for. Since it is not a large physiotherapy practice, but only 1 to a maximum of 2 people are there, the 2 rooms are sufficient. A separate additional changing room is not necessary. But how can these 2 rooms, 15 + 8 sqm + 2-5 sqm storage room + reception, be best planned with the floor plan? Unfortunately, the bathroom in the corner has to remain there. Unfortunately, not much can be done at the front door, at most it can be turned if necessary.

How about this?
You could make "Schlafen" a bit smaller by moving the left wall to the right.

Edit: I forgot the storage room. Need to reconsider.

And what is so difficult now to answer the questions from @ypg and me? What happens in the rooms? What absolutely has to go in and is it used?

I'm out! .. guilty with 2 words and 30 characters!